The research described in this proposal aims to study the mechanisms by which diet composition and regular exercise influence basal and insulin- stimulated muscle glucose uptake (MGU) in vivo. MGU will be assessed in terms of three serial steps: delivery to glucose to the muscle, transport of glucose across the sarco-lemma, and phosphorylation of glucose intracellularly. Each of these steps has been studied in isolation, and much is known about their regulation. These protocols bridge the biochemical and hemodynamic observations with the whole body measurements of insulin action made in healthy and insulin resistant states. The experimental model used is the conscious rat, fed chow or a high fat diet that produces insulin resistance. In some protocols, rats will undergo exercise training, an intervention which increases insulin-stimulated MGU. The control of MGU will be assessed in vivo using novel isotopic (3-0[3H]methylglucose, [U-14C]mannitol,2-deoxy- [3H]glucose) techniques in combination with methods for sampling blood and tissues and measuring hemodynamics. The thread that links the proposed experiments is that the control of MGU is distributed between glucose delivery, transport and phosphorylation. An extension of this distributed control is that conditions of insulin resistance or increased insulin action can be caused at each step involved in the control of MGU. The specific aims of the proposed experiments are to determine in the whole organisms: 1) The key site(s) of regulation (extracellular, sarcolemma, intracellular) of MGU in chow-fed rats and the site(s) that are dysfunctional in rats made insulin resistant by high fat feeding; 2) The mechanism(s) by which insulin-stimulated MGU is improved following exercise training; 3) The mechanism(s) by which muscle morphological differences due to fiber type affect MGU; and 4) How barriers to MGU correspond to and are affected by hemodynamics and the expression and compartmentation of the primary skeletal muscle isozyme of hexokinase. The hope is that, by identifying sites of regulation and dysfunction, these studies will allow optimal sites of therapy to be identified and targeted so that people with insulin resistance can be treated most effectively.